The combustion air required for internal combustion engines is generally filtered before being supplied to the combustion chamber in order to increase the efficiency and the service life of the internal combustion engine. For filtration of the combustion air generally an air filter arrangement is used. This is important in particular in connection with internal combustion engines that operate in an environment that is subject to special pollution loading of the ambient air, for example, in the field of the construction industry or agriculture. In particular in the field of the construction industry or in agriculture at times a very high dust loading occurs that requires filtering of the combustion air. Because of the fact that the spectrum of dust particle size generally is not known beforehand, an air filter arrangement must be designed such that all particle sizes that can interfere with the operation of the internal combustion engine in any way can be reliably filtered out in order to enable a supply of sufficiently clean combustion air to the internal combustion engine.
In particular in the field of internal combustion engines that are used in or on vehicles the configuration of an efficiency-optimized and space-optimized air filter system is mandatory in order to keep the dimensions small and in order to still enable a high efficiency of the air filter arrangement, on the other hand.
For example, EP 1 364 695 A1 discloses an air filter that is integrated into the intake manifold of an internal combustion engine in order to subject the combustion air to be supplied to the cylinders of the internal combustion air to a filtration action. The air filter is substantially of a three-par configuration and comprises a filter element in a filter housing which filter element is configured as an exchangeable filter cartridge through which combustion air flows axially and that is insertable radially by means of a closable lid into the filter housing. The filter cartridge has arranged upstream thereof a cyclone preseparator that serves for separation of large dirt particles. Downstream of the filter cartridge there is a secondary or fine filter element that also is insertable radially into the filter housing when the lid is open. The cyclone preseparator, the filter cartridge, and the fine filter element are positioned axially sequentially behind one another and the combustion air to be filtered passes through them without deflection in the axial direction.
One of these possibilities is the configuration of the main filter element in the form of a folded bellows filter. For example, a folded bellows can be comprised of a star-shaped folded filter element whose filter folds extend in radial direction wherein the front edges of the filter folds extend substantially in an axial direction. Such a folded bellows filter is disclosed, for example, in WO 2008/067030 in which the filter element is comprised of a folded filter bellows wherein the front edges of the filter folds extend in the axial direction that corresponds to the direction of flow while the filter folds extend in a direction transverse thereto. This folded bellows is comprised of a multiple folded bellows that provides on a limited axial section or on a section in the flow direction an increased filter surface area in order to increase in this way the filtering capacity.